Effect of ω-assisted precipitation on β→α transformation and tensile properties of Ti-15Mo-2.7Nb-3Al-0.2Si alloy

Microstructure and tensile properties of Ti-15Mo-2.7Nb-3Al-0.2Si alloy subjected to single and duplex aging treatments were investigated. The single aging treatment was carried out at 500 °C for 8 h. The duplex aging treatments was performed at 320 °C for 2 h for the first step, and the second step was carried out as the single treatment. As for microstructure, researches indicated that the precipitation formed during aging treatments was affected by phase transformation courses. Different from the needle-like α precipitates of β matrix during the single aging treatment, the finer shuttle-like α precipitates during the duplex aging treatment was obtained due to the assistance of ω phase formed in the first step aging. EBSD analysis showed that the orientation of precipitation was similar no matter with the single aging or the duplex aging treatment. The higher ultimate tensile strength value of 1437 MPa was obtained through strengthening of shuttle-like α phase with a length of 0.5 μm in the duplex aging treatment, with an acceptable elongation of 10.6%. The tensile fracture of those aging treatments illustrated that deep dimples in the duplex aging sample were beneficial for the higher strength.